Silicon carbide (SiC) represents a promising semiconductor material, which allows for higher power devices and higher frequency applications than known silicon devices. However, different manufacturing processes are needed for creating doped layer in silicon carbide substrates and for forming electrical contacts.
Prior art Junction Barrier Schottky (JBS) diodes comprise a cathode electrode, on which the following layers are arranged: an n doped cathode layer, a lower n-doped drift layer, a higher p+ doped anode layer. All doped layers are formed as doped silicon carbide layers. The anode layer is in contact to an anode electrode, which thus forms an ohmic contact to the anode layer. The anode electrode is formed as a continuous metal layer over the whole surface of the device. The drift layer extends to the surface of the silicon carbide. This layer has a Schottky contact to the anode electrode.
Thus, on the anode side of the device, a Schottky metal contact is deposited on top of the SiC drift layer associated to p+ implants for the anode layer, which are in close proximity to the Schottky junctions such that its depletion region under reverse bias creates a potential barrier to shield the Schottky junction from high electrical field, thus reducing leakage current.
Anode electrodes for prior art SiC Junction Barrier Schottky diodes are formed through the deposition of metal layer (typically Ti) on top of SiC n-type lightly doped drift layer and p+ implants. The metal layer is then annealed at maximum temperature below 700° C. in order to avoid degradation of the Schottky contacts or even ohmic contact formation in the Schottky regions, since ohmic contact formation occurs at more than 1000° C. in SiC.
However, such low temperature range is insufficient to form ohmic contact to the p+ anode layer even though it is highly doped.
Although the ohmic contact formation can be performed using extra deposition, annealing and lithography steps in order to first form the ohmic contact at high temperature followed by formation of the Schottky contact at low temperature, this would increase costs, and the conductive Schottky contact is inevitably compromised due to the lack of efficient selective cleaning of the areas dedicated as Schottky contact areas after the creation of the ohmic contacts, because such a cleaning, typically a wet cleaning also affects the ohmic contact.
In U.S. Pat. No. 8,450,196 B2 a manufacturing method id described, in which on a SiC substrate, a continuous metal layer is formed over the whole surface of the substrate (creating a Schottky contact). Afterwards, a mask having openings is applied, and the metal layer is irradiated through the mask. As a result, at such places, at which the mask has openings, a high temperature can be applied to the metal layer, which converts the Schottky contact to an ohmic contact so that Schottky and ohmic contacts alternate. However, this method leads to poor accuracy and resolution due to the diameter of the heat beam defining the minimum size of the ohmic contacts and due to heat spreading in the metal layer the heat distributes to the lateral sides of the beam so that the interface between the ohmic contact and the Schottky contact becomes fuzzy.
JP 2011 165 660 A describes a method for creating a Schottky barrier diode. On p anode regions, a 30 nm Titanium and 100 nm Nickel layer is deposited. Between the p anode regions, a thick metal layer made of Molybdenum is deposited, which also covers the Ti/Ni metal layers, thus forming a common planar surface on the anode side. Now, all metal layers are simultaneously treated at a high temperature. Due to the usage of different metals, an ohmic joining layer is formed from the Ti/Ni layer and a Schottky barrier layer is formed from the Molybdenum layer.
EP 1 885 000 A2 describes a JBS Schottky diode, which has p+ and p doped regions. Due to the different doping concentrations of the p doped regions, an ohmic contact is formed on the heavily doped p+ regions, whereas in between these regions Schottky contacts are formed on the lowly doped p regions.